In an electrophotographic modular printing machine of known type, such as for example the NexPress 2100 printer manufactured by NexPress Solutions, Inc., of Rochester, N.Y., color toner images are made sequentially in a plurality of color imaging modules arranged in tandem, and the toner images are successively electrostatically transferred to a receiver sheet adhered to a transport web moved through the modules. Commercial machines of this type typically employ intermediate transfer members in the respective modules for the transfer to the receiver member of individual color separation toner images. However, the invention as described herein also contemplates the use of tandem and other electrostatographic printers that do not employ intermediate transfer members but rather transfer each color separation toner image directly to the receiver.
Electrostatographic printers having a three, four, or more color (multi-color) capability are known to also provide an additional toner depositing station for depositing clear toner. The provision of a clear toner overcoat to a color print is desirable for providing protection of the print from fingerprints and reducing certain visual artifacts. However, a clear toner overcoat will add cost and may reduce color gamut of the print, so it is desirable to provide for operator/user selection to determine whether or not a clear toner overcoat will be applied to the entire print. In U.S. Pat. No. 5,234,783, issued on Aug. 10, 1993, by Yee S. Ng, it is noted that in lieu of providing a uniform layer of clear toner, a layer that varies inversely according to heights of the toner stacks may be used instead as a compromise approach to even toner stack heights. As is known, the respective color toners are deposited one upon the other at respective locations on the receiver and the height of a respective color toner stack in the sum of the toner contributions of each respective color and provides the print with a more even or uniform gloss.
It is recognized that a multi-color image forming process that employs a clear toner overcoat provides for prints with a color gamut that is relatively compromised. However, the use of such clear toner is desirable to improve abrasion resistance of prints. It would therefore be desirable to provide a method and apparatus that unexpectedly achieves an improved color gamut with application of clear toner, and substantially maintains the benefits of print protection provided by the presence of the clear toner overcoat.